1. Field of the Invention
This invention relates to an angle-of-rotation sensor for detecting the angle of rotation of a shaft. This invention particularly relates to an angle-of rotation sensor for detecting the angle of rotation of the crankshaft of an internal combustion engine of an automobile or other such vehicle.
2. Description of the Prior Art
Recently, electronic control technology for internal combustion engines has been making rapid progress. With respect to such electronic control, control timing is important and as such it is necessary to detect with precision piston crank angle positions for use as reference signals. Conventional types of angle-of-rotation sensors include, for example, the type disclosed in Japanese Laid-open Patent Publication No. 57(1982)-133311. In this conventional technology a rotating member is formed by stacking three disk-shaped magnets one on top of the other. Each of the magnets has magnetic poles formed contiguously around the periphery thereof, forming three arrays of magnetized zones. However, because in such an arrangement the magnetized zones are in close, continuous contact in the direction of the axis of rotation with non-magnetized zones provided therebetween, there is a risk of magnetic interference arising between the magnetized zones, and the magnetic flux path of one magnetized zone disturbing the magnetic poles of an adjacent magnetized zone and the magnetic force thereby produced giving rise to detection errors, for which reason it has not been possible to detect accurately the crank angle position. The risk becomes particularly strong when a high-sensitivity device such as a magneto resistor is used as the detection means.
In addition, because in this conventional type the rotating member is formed by stacking together disk-shaped magnets, the rotating member becomes heavy, so the diameter of the shaft has to be increased, with the result that other parts such as the bearings have had to be made large, so that overall the sensor becomes large and heavy, requiring a large space to house it in and causing a degradation in durability.